I'm worried that a lot of other ports will pick this up if installed. 'grep -wiR alsa' over build logs suggests it's in the order of a hundred ports - apart from the problem of missing deps, we don't want it taking priority over native sndio support in applications.
Unless installed in a way to make it hard to pick up accidentally (e.g. a non-standard directory, which has its own problems) I expect the amount of work needed to cope with this in the rest of the ports tree is likely to be quite a lot more than that needed to port a couple of applications from alsa to sndio.
